As is well known to persons involved in the electric power industry, power transmission losses are minimized when a zero phase relationship (e.g., a zero phase angle) exists between the current and voltage waveforms of the power being transmitted. In order to achieve this phase relationship capacitors are connected to power lines. In order to determine the amount of capacitance to be added, it is necessary to determine the phase angle between the current and voltage waveforms. In the past, this has been accomplished by installing current and voltage transformers at various locations in the power distribution system. The signals produced across the secondary windings of such transformers are utilized to determine the phase angle. This technique has a number of disadvantages. First, the inclusion of current and voltage transformers is expensive, particularly if phase information is desired at frequent intervals along the transmission line. Not only is the cost of the transformers undesirably high, the installation and maintenance of such transformers is time consuming and, therefore, expensive. Further, the inclusion of such transformers may disturb the operation of the power distribution system in an undesirable manner.
In order to avoid the foregoing disadvantages, attempts have been made to produce portable phase angle meters suitable for use on high voltage power lines. One such approach is described in U.S. Pat. No. 4,316,254 entitled "Portable Phase Angle Meter Instrument" by Harry P. Levin. One of the major disadvantages of portable phase angle meters of the type described in U.S. Pat. No. 4,316,254 is its requirement that a coupling connection be made to two high voltage power line conductors, rather than a single power line conductor. More specifically, the instrument described in U.S. Pat. No. 4,316,254 includes a potential probe for making a coupling connection to a first conductor and a current probe for making a coupling connection to a reference conductor. The instrument produces current and voltage signals that are digitized and processed to generate leading and lagging phase angle signals. The phase angle signals are applied to a suitable display. The probes include hollow tubes of plastic or other nonconductive materials. These power line "hot sticks" support hooks, which are used to hang the probes from the high voltage power line conductors. Obviously, for safety reasons, it is desirable to minimize the number of connections to high voltage power line conductors required to obtain desired measurements. Also, obviously, the minimum number of connections is a single connection. Consequently, a portable phase angle meter of the type described in U.S. Pat. No. 4,316,254 has the disadvantage of requiring more than a minimum number of connections to high voltage power lines.
Therefore, there is a need for a new and improved portable phase angle measuring instrument suitable for use with high voltage power lines. In particular, there is a need for a portable phase angle measuring instrument that only requires a single coupling connection to a high voltage power line conductor.
In addition to phase angle measuring, in many instances, power transmission compound personnel require information about the RMS value of the current flowing through the line and/or the value of the reactive current in the power transmission line. Therefore, it is desirable to provide a high voltage power line measuring instrument that determines such current information as well as phase angle information.